1. Field of the Invention
This invention relates generally to pressurized containers, and more particularly, to a gas storage and delivery system for restoring and maintaining pressure as it is depleted from pressurized containers such as aerosol dispensers, bottles of carbonated beverage, and the like.
2. Prior Art
Pressurized containers are commonly used to dispense many products, including paint, lubricants, cleaning products, hair spray, and food items. These containers are typically aerosol dispensers in which the product is stored under pressure with a suitable propellant. Dispensing of the product occurs when a discharge nozzle is depressed, permitting the pressurized product to be forced out through the nozzle, usually as a spray, stream or foam. As product is depleted from the container, the pressure exerted by the propellant decreases, especially evident with compressed gases, and may become diminished to the extent that all of the product cannot be dispensed from the container, or desired characteristics are not achieved.
Many products, e.g., hair spray, require a carrier in addition to the propellant component, e.g., alcohol, that dries quickly upon discharge from the container. Volatile organic compounds (VOCs) such as propane, isobutane, dimethyl ether, and the like, are suitable as propellants for many products, but their use is limited due to environmental concerns. For instance, under some current regulations no more than 55% of the contents of the container can comprise a VOC. In an aerosol dispenser, as much as 25% of the VOC could be required for use as a propellant, leaving about 30% VOC in the product. This 25% reduction typically is made up with water, which does not dry as quickly as the VOC, resulting in a xe2x80x9cwetxe2x80x9d product when used.
Carbon dioxide (CO2) is environmentally friendly, and is therefore useful as an aerosol propellant, but its use has been limited due to the drop off in pressure from start to finish as the product is used. For example, in a typical situation the starting pressure might be 100 psig and the finishing pressure only 30 psig. At this low finishing pressure all of the product may not be discharged, and/or proper aerosolization may not be obtained.
Carbonated beverages are also bottled under pressure, usually by a pressurized inert gas, such as CO2, placed in the bottle along with the beverage. Over time, the pressure of the gas may decrease, resulting in a xe2x80x9cflatxe2x80x9d drink. This is particularly true when plastic containers are used to bottle carbonated beverages. The shelf life of such products may be undesirably short.
Further, cans of pressurized gas are provided for cleaning dust and the like from sensitive equipment, such as computers, computer keyboards, etc., by blowing a pressurized stream of propellant onto the equipment. Currently available products for this purpose use a VOC (e.g., Dymel(copyright) by DuPont) as the propellant. These materials are relatively expensive for the intended use.
Accordingly, there is a need for a system to replenish and maintain a desired pressure in pressurized containers, such as aerosol dispensers and carbonated beverages, and particularly to such a system that is inexpensive and environmentally friendly.
The present invention provides a system and method to replenish and maintain a desired pressure in pressurized containers, such as aerosol dispensers and carbonated beverages.
In accordance with the invention, a gas storage system is employed in pressurized containers to store and release gas to replenish pressurized gas depleted from the container. More particularly, the invention uses a material that is capable of adsorption and storage of a large quantity of gas, and then releasing it under predetermined conditions. Additionally, the material of the invention is a non-toxic material.
The storage body used in the invention is known as a pressure swing adsorption (PSA) system, wherein adsorption of gas into the body occurs at a high pressure, and desorption of gas from the body occurs at a low pressure. Such adsorption/desorption devices are capable of storing under pressure a volume of gas that is 18 to 20 times the volume of the body.
For example, the invention may use a storage body made from granular activated carbon, or a carbon fiber composite molecular sieve (CFCMS) material, to adsorb and store a quantity of a desired gas, such as nitrous oxide or carbon dioxide, for example. The storage body may be pre-charged with the desired gas and then placed in a pressurized container, or in communication with the interior of the container, or it may be placed in a container and a desired gas introduced under pressure into the container to charge the storage body, for subsequent release of the gas as the propellant or carbonization gas becomes depleted, thereby restoring the pressure in the container to a desired level.
A mass of granular activated carbon may be formed into a cohesive shape such as a ball or cube or the like which is simply placed in the container, or the mass of activated carbon may be encased in a film or cover. The cover may be something that functions only to contain the carbon and prevent its admixture and discharge with the product, or it may be a gas permeable membrane that is capable of passing the desired gas but prevents contact between the carbon and the liquid or other product in the container. One suitable source of granular activated carbon, for example, is a 10xc3x9750 mesh material available from Westvaco Corporation under number 1072-R-99. One suitable film may comprise a Tetratex(copyright) 1316 membrane film, for example, available from Tetratec PTFE Technologies.
For some applications, nitrous oxide may be used in lieu of or in combination with carbon dioxide. Nitrous oxide is more compatible with products having an oil component, for example.
An alternative storage body can comprise a carbon fiber composite molecular sieve (CFCMS) material, as disclosed in U.S. Pat. Nos. 5,912,424 and 6,030,698, which are incorporated in full herein.
During filling of an aerosol container, the storage body may be placed in the container and a suitable propellant gas introduced into the container to a pressure of 150 psig, for example, whereupon the body will adsorb 75 psig, for example. Product is then introduced into the container, increasing the pressure back up to 80 to 100 psig, for example. As product is expelled, gas is released from the body to restore the pressure in the container to a desired predetermined level.
The body may have any desired shape, such as spherical, tubular, cubic, etc., and may have any desired suitable size to store and release an appropriate amount of gas during use of the system. Further, the carbon material may be enclosed within a suitable membrane for one-way flow of the gas out of the material and through the membrane into the container, while precluding direct contact between the product and the carbon. Such membranes are employed in reverse osmosis water purification systems, for example.
The gas storage and release system of the invention may also be used to discharge oxygen or another gas into a beverage, such as bottled water or a sports drink, if desired.
In essence, the invention comprises the use of a gas adsorption material in a pressurized container as a reservoir for a gas such as carbon dioxide, nitrous oxide, and the like, and which releases the gas into the container as the pressure in the container decreases as product is dispensed, thus maintaining a desirable pressure in the container and obtaining a more uniform product discharge from beginning to end.
The use of activated carbon to adsorb additional gas in an aerosol container can increase the available gas to a level which results in the pressure remaining more uniform until the product is depleted. This, in turn, maintains a more consistent, uniform and acceptable spray pattern from beginning to end because the pressure at the end is very close to the starting pressure.
The carbon dioxide can be used alone or in combination with other gases, such as nitrous oxide, or the nitrous oxide can be used alone or in combination with other gases, and/or any one or all of these can be used in combination with liquified compressed gases such as propane, isobutane, dimethyl ether or Dymel(copyright) (trademark of DuPont), to produce desired spray patterns which would permit reduction in the quantity of volatile organic compounds used in the pressurized product.